There's a newly active coalition partner taking the fight to ISIS: Turkey. That might seem like good news. But really, it ought to be a dark reminder of how messed up the Middle East really is.

In the waning decades of its centuries-long run, the Ottoman Empire was derisively known as the Sick Man of Europe. And its death at the hands of the Allied powers in World War I gave birth to a nightmare. The old imperium, held together by Islam, gave way to a new patchwork of nation-states —...